1. Field of the Invention
This invention relates to integrated circuit (IC) packaging technology, and more particularly, to an Integrated Circuit packaging method for packaging an Integrated Circuit chip of an optically-sensitive type, such as an image-sensor Integrated Circuit chip, which can help prevent resin flash on lead frame and help increase wire bondability.
2. Description of Related Art
Integrated Circuit packaging technology is used to pack one or more Integrated Circuit chips in a single module. Typically, the Integrated Circuit chip or chips are enclosed within an opaque encapsulating body, and thus is invisible from the outside. However, for image-sensor Integrated Circuit chips, it is required to allow them to detect outside light to serve their function. For this reason, a special Integrated Circuit package configuration is used to pack Integrated Circuit chips of optically-sensitive types.
One problem to the manufacture of the image-sensor Integrated Circuit chips, however, is that the resin used to form the package body could easily flash onto the lead frame surface, which would then undesirably degrade the quality of the die attachment and wire bonding on the lead frame surface in subsequent processes. Conventionally, various Integrated Circuit packaging methods have been proposed to eliminate the flash problem, including, for example, the U.S. Pat. No. 5,070,041 and the U.S. Pat. No. 5,523,608.
The U.S. Pat. No. 5,070,041 discloses an Integrated Circuit packaging method for manufacturing a single-chip image-sensor Integrated Circuit package, which is briefly depicted in the following with reference to FIGS. 1A-1D.
Referring to FIG. 1A, by the U.S. Pat. No. 5,070,041, the first step is to prepare a lead frame 110 of the type having a die-pad portion 111 and a finger portion 112. To prevent flash, a polymer precoating 120 is formed over the die-pad portion 111 and the inner end of the finger portion 112.
Referring further to FIG. 1B, in the next step, a molding process is performed to form a top package body 121 and a bottom package body 122. The top package body 121 is centrally-hollowed for die attachment. During this molding process, however, the resin used to form the top and bottom package bodies 121, 122 would undesirably flash onto the die-pad portion 111 and the inner end of the finger portion 112 of the lead frame 110 (the flashed resin is here pointed out by the reference numeral 130). Since these lead frame portions are pre-coated with the polymer precoating 120, the flashed resin 130 thereon can be subsequently removed by using a special solvent.
Referring further to FIG. 1C, in the next step, a die-attachment process is performed to attach an image-sensor Integrated Circuit chip 140 on the die-pad portion 111 of the lead frame 110. Subsequently, with the bottom package body 122 being fixed over a heat block 150, a wire-bonding process is performed to apply a set of bonding wires 160 for electrically coupling the image-sensor Integrated Circuit chip 140 to the inner end of the finger portion 112 of the lead frame 110.
Referring further to FIG. 1D, in the next step, a lidding process is performed to cover a transparent lid 170 onto the top opening of the top package body 121 to thereby hermetically seal the image-sensor Integrated Circuit chip 140. This completes the manufacture of the single-chip image-sensor Integrated Circuit package.
The foregoing Integrated Circuit packaging method, however, has two drawbacks. First, it is quite costly to implement the forming of the polymer precoating 120 and the subsequent solvent cleaning of the flashed resin 130 over the polymer precoating 120, which makes the overall manufacture process quite cost-ineffective. Second, during the wire-bonding process, since the heat block 150 is in direct thermal contact with the resin-made bottom package body 122 rather than with the lead frame 110, the heat transfer from the heat block 150 to the lead frame 110 would be inadequate, thus undesirably resulting in a poor bondability to the bonding wires 160. There exists therefore a need for a new Integrated Circuit packaging method that can eliminate the flash problem in a more cost-effective way and also allows a better heat transfer to the die pad during the wire-bonding process.
The U.S. Pat. No. 5,523,608 discloses an Integrated Circuit packaging method used to manufacture a dual-chip image-sensor Integrated Circuit package, which is briefly depicted in the following with reference to FIGS. 2A-2D.
Referring to FIG. 2A, by the U.S. Pat. No. 5,523,608, the first step is to prepare a lead frame 210 of the type having a die-pad portion 211 and a finger portion 212. Next, a first die-attachment process is performed to attach a first Integrated Circuit chip 241 on the back side of the die-pad portion 211 of the lead frame 210. After this, a first wire-bonding process is performed to apply a first set of bonding wires 261 for electrically coupling the first Integrated Circuit chip 241 to the back side of the inner end of the finger portion 212 of the lead frame 210.
Referring further to FIG. 2B, in the next step, a molding process is performed to form a top package body 221 and a bottom package body 222. The top package body 221 is centrally-hollowed for die attachment. During this molding process, however, the resin used to form the top and bottom package bodies 221, 222 would undesirably flash onto the front side of the die-pad portion 211 and the inner end of the finger portion 212 of the lead frame 210 (the flashed resin is here pointed out by the reference numeral 230). A blast process is then performed by the use of a blaster 231 to clean the flashed resin 230 away.
Referring further to FIG. 2C, in the next step, a second die-attachment process is performed to attach a second Integrated Circuit chip 242 (image-sensor Integrated Circuit chip) on the front side of the die-pad portion 211 of the lead frame 210. Subsequently, with the bottom package body 222 being fixed over a heat block 250, a second wire-bonding process is performed to apply a second set of bonding wires 262 for electrically coupling the second Integrated Circuit chip 242 to the front side of the inner end of the finger portion 212 of the lead frame 210.
Referring further to FIG. 2D, in the next step, a lidding process is performed to cover a transparent lid 270 onto the top opening of the top package body 221 to thereby hermetically seal the second Integrated Circuit chip 242. This completes the manufacture of the dual-chip image-sensor Integrated Circuit package.
The foregoing Integrated Circuit packaging method, however, also has two drawbacks. First, it is quite costly to implement the blast process to clean the flashed resin, which makes the overall manufacture process quite cost-ineffective. Second, during the second wire-bonding process, since the heat block 250 is in direct thermal contact with the resin-made bottom package body 222 rather than with the lead frame 210, the heat transfer from the heat block 250 to the lead frame 210 would be inadequate, thus undesirably resulting in a poor bondability to the second set of bonding wires 262. There exists therefore a need for a new Integrated Circuit packaging method that can eliminate the flash problem in a more cost-effective way and also allows a better heat transfer to the die pad during the second wire-bonding process.
It is the primary objective of this invention to provide a new Integrated Circuit packaging method which can help solve the above-mentioned flash problem.
It is another objective of this invention to provide a new Integrated Circuit packaging method which allows the lead frame to come in direct thermal contact with the heat block during wire-bonding process.
In accordance with the foregoing and other objectives, the invention proposes a new Integrated Circuit packaging method for image-sensor Integrated Circuit chips. The Integrated Circuit packaging method of the invention can help prevent resin flash on the die-pad portion and the inner end of the finger portion of the lead frame. This benefit allows the die attachment on the die-pad portion to be more reliable than the prior art. Moreover, the Integrated Circuit packaging method of the invention allows lead frame to come into direct thermal contact with heat block during wire-bonding process, so that it allows an increased level of bondability to the bonding wires, making the Integrated Circuit package more assured in quality and more reliable to use than the prior art.